A system for ultrasonic computed tomography (UCT) of attenuation and speed of ultrasound propagation along with simultaneous pulse echo imaging of the same place has been developed and is currently undergoing clinical evaluation. The speed and reliability of the patient studies will be enhanced by their performance at the Breast Cancer Detection Center of the University of Michigan. Use of large, focused transducers has provided high resolution in pulse echo and attenuation images of the breast, and use of separate small transducers has provided state-of-the-art speed of sound images. Studies on patients and normal volunteers have allowed development of images with surprising detail and have revealed the complementary relations between pulse echo images and ultrasonic attenuation and speed of sound images. Nintey-five patients have been imaged thus far with ultrasonic CT, while pulse echo imaging in the same planes as the UCT has been performed on 20 of the most recent patients. Quantitative analysis of attenuation and speed of sound in various lesions and normal tissues is in progress. Development of phase independent imaging of ultrasonic attenuation as well as development of UCT images with improved resolution and quantitative accuracy is proposed.